Study On Preparation And Properties Of Ethylene Vinyl Acetate-Polystyrene Copolymer By Suspending Grafting

EVA-g-PS graft copolymers were prepared by using pre-irradiation EVA and styrene (St) as the main starting materials via suspension graft copolymerization. The effects of reaction temperature, reaction time, ratio of materials and BPO concentration on degree of grafting were studied. The structure of graft copolymer was characterized by means of Fourier transform infrared spectroscopy (FTIR),1H nuclear magnetic resonance (1H-NMR), Raman spectrum and X-ray photoelectron spectroscopy (XPS). The FTIR spectra of EVA-g-PS showed some new peaks at700cm-1,755cm-1,1480cm-1,1602cm-1and3060cm-1compared to EVA, and the Raman spectra of EVA-g-PS showed more obviously new peaks at1632cm-1,1150-1250cm-1,1060cm-1,1002cm-1. These peaks were attributed to C-H bond and C=C double bond from benzene ring. The’H-NMR spectra of EVA-g-PS showed five new chemical shift peaks at6-8ppm which were attributed the H from benzene ring. These results indicated that St has been successfully grafted onto EVA molecular chains.The thermal properties of EVA-g-PS were studied by using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). With increasing degree of grafting, the melt temperature (Tm) and the crystallization temperature (Tc) decreased, the thermal stability of the graft copolymer also decreased. Because PS grafted onto EVA molecular chains, the perfection of EVA molecular chains regularity were destroyed, which would lead to the reduction crystallization capability of EVA-g-PS. Dynamic mechanical analysis (DMA) results indicated that the glass temperature (Tg) increased with increasing degree of grafting. Dielectric analysis results indicated that with increasing degree of grafting dielectric constant (ε) increased, dielectric losses (tan δ) decreased. Molecular weight and molecular weight distribution (MWD) of EVA and EVA-g-PS were determined by gel permeation chromatography (GPC). It was found that molecular weight of the copolymer was higher than that of EVA, while the molecular weight distribution was no obvious change. The rheological properties of EVA and EVA-g-PS were investigated, and found that the storage modulus, the loss modulus and the complex viscosity of EVA-g-PS were higher than that of EVA at low frequency. While in high frequency range, they were similar. And with increasing frequency, the storage modulus and the loss modulus increased, while the complex viscosity decreased. Morphology structure of EVA and EVA-g-PS were investigated by using transmission electron microscope (TEM). Comparing with EVA, EVA-g-PS showed that the C=C double bond increased and well-distributed. Mechanical properties were measured, that compared with EVA, the values of tensile strength and elongation at break were decreased, while the value of Young’s modulus was increased with increasing degree of grafting.